Natural oils can be refined, e.g., in a biorefinery, by cross-metathesizing the glyceride or a transesterified derivative thereof with a short-chain olefin. When the short-chain olefin is a C2-4 olefin, the refining process yields a predominant amount of C10-12 esters and olefins. The product stream contains a variety of other compounds, however. Many of these compounds are relatively non-volatile and cannot be easily separated by fractional distillation. In some instances, these materials can remain in the distillation pot. These materials can be referred to as the “pot bottoms” or “bottoms” from the fractionating process. The pot bottoms can also include other waste materials from the metathesis process, such as heavy metals and other compounds that may be present in the oil (e.g., colored impurities).
In many instances, this bottoms stream may contain certain compounds or combinations of compounds that have economic value because of their utility in certain applications. Therefore, it may be desirable to carry out various treatments on the bottoms stream to yield compounds or compositions that can be used in various applications.
In many instances, the bottoms stream can contain certain colored impurities, such as carotenes, which can interfere with the ultimate utility of the composition. It can be desirable to treat the composition chemically to decolorize the composition, e.g., be chemically transforming the colored species to compounds that are not colored. Some methods of decolorizing the composition may also react with the valuable materials in the composition and thereby decrease the value of the bottoms stream. In the context of refining a natural oil, the bottoms stream contains some mixture of olefins and esters (including both mono-esters and di-esters). Therefore, it may be desirable to decolorize the composition in a manner that does not react with these compounds in a way that substantially lowers their economic value. In some instances, a mixture of chromic and sulfuric acids can be used. But this has certain disadvantages, primarily related to the use and disposal of hexavalent chromium. Therefore, there is a need to develop additional ways of decolorizing a biorefinery bottoms stream, so as to reduce the color without substantially affecting the value of the olefins and/or esters in the stream.